A Broadband Distributed Amplifier Extending the Operation Frequency to 0.944fT

This paper presents an ultra-broadband distributed amplifier (DA) with operation frequency from dc to 0.944fT. A novel gain cell of improved Dalington cascode with stacked transistor is proposed. The gain of proposed gain cell at high operation frequency is dramatically improved since the gain roll-off at high operation frequency caused by parasitic capacitances of transistors are suppressed by the nature of topology. The proposed gain cell along with several gain-peaking techniques, the gain bandwidth of DA is significantly extended. The presented DA is fabricated by using 0.25-μm GaAs E/D-mode pHEMT process with the 57-GHz transition frequency(fT). Measurement results indi-cate that the implemented DA obtains a 11.5-dB average gain, better than 8-dB input/output return loss, and 14.8-dBm typical saturated output power from the dc to 53.8 GHz (0.944fT). To the best of authors’ knowledge, the implemented DA achieves largest ratio of bandwidth to fT among the DAs using similar process.